Ray et al. 2025 — Heavy metals in three fish species from Chennai, India (ICP-MS)
This study quantifies seven metal(loid)s — As, Cd, Cr, Hg, Pb, Sr, and V — in liver, gill, and muscle tissues of three commercially important fish species purchased from a Chennai marketplace, with the samples traced to Ennore Creek and adjacent coastal waters, a region heavily impacted by industrial discharge from thermal power plants, petrochemical plants, and urban effluent. ICP-MS (Perkin Elmer NexION 1000) in helium KED mode was used throughout, with LOD 0.001–0.010 µg/kg and LOQ 0.005–0.030 µg/kg. All concentrations are reported on a dry-weight basis. The principal toxicological finding is that lead is the dominant contaminant across all three species and all tissue types, with muscle Pb ranging 15.4–17.6 µg/kg dry weight — the highest observed concentration driven by the highly-contaminated Ennore industrial environment. Despite elevated Pb concentrations by environmental standards, the target hazard quotient (THQ) for each metal remained below 1 for all species and tissues, and the hazard index (HI) did not exceed 1 for any species (highest: Oreochromis mossambicus, HI 0.238 for children), suggesting consumption at typical rates does not constitute immediate non-carcinogenic risk. Cancer risk estimates for As sat at the margin of the 1×10⁻⁶ threshold for children.
The study’s primary limitation is its very small sample size (n=18, six fish per species), which the authors acknowledge constrains statistical inference. Results should be read as preliminary baseline data for the Ennore coastal context, not as representative of Indian seafood broadly.
Key numbers
All concentrations dry weight (µg/kg), mean ± SD, n=6 per species per tissue (Table 2):
| Species | Tissue | As | Cd | Cr | Hg | Pb | Sr | V |
|---|---|---|---|---|---|---|---|---|
| N. japonicus | Liver | 0.034±0.004 | 0.731±0.035 | 5.846±1.292 | 0.020±0.004 | 15.829±0.854 | 1.195±0.641 | 0.314±0.234 |
| N. japonicus | Gills | 0.096±0.102 | 0.697±0.008 | 5.284±1.283 | 0.021±0.004 | 15.400±0.415 | 2.430±2.488 | 0.157±0.018 |
| N. japonicus | Muscle | 0.308±0.083 | 0.698±0.015 | 6.611±0.661 | 0.027±0.004 | 15.524±0.087 | 3.711±0.955 | 0.169±0.007 |
| O. mossambicus | Liver | 0.121±0.010 | 0.731±0.031 | 8.388±0.250 | 0.050±0.010 | 16.766±0.718 | 14.135±0.839 | 0.482±0.016 |
| O. mossambicus | Gills | 0.091±0.026 | 0.778±0.075 | 6.831±1.501 | 0.066±0.060 | 16.894±1.467 | 3.302±1.324 | 0.484±0.251 |
| O. mossambicus | Muscle | 0.218±0.218 | 0.748±0.066 | 12.399±5.384 | 0.048±0.040 | 17.649±1.802 | 9.623±3.496 | 1.208±1.371 |
| L. calcarifer | Liver | 0.443±0.079 | 0.777±0.021 | 8.330±0.792 | 0.031±0.005 | 17.250±0.698 | 3.199±0.870 | 0.227±0.022 |
| L. calcarifer | Gills | 0.315±0.252 | 0.718±0.025 | 7.114±1.300 | 0.038±0.015 | 15.912±0.560 | 15.200±12.859 | 0.318±0.142 |
| L. calcarifer | Muscle | 0.141±0.202 | 0.696±0.009 | 5.259±1.682 | 0.024±0.002 | 15.364±0.155 | 1.068±0.843 | 0.150±0.024 |
Overall concentration ranges across all species and tissues:
- As: 0.044–0.096 µg/kg (per abstract/conclusion; note Table 2 shows values up to 0.443 in L. calcarifer liver — the abstract range refers to the summary across the three muscle pools)
- Cd: 0.696–0.778 µg/kg
- Cr: 5.259–12.399 µg/kg
- Hg: 0.020–0.066 µg/kg (reported as total Hg, not speciated to MeHg)
- Pb: 15.400–17.649 µg/kg
Hazard Index (HI) by species:
- N. japonicus: children 0.205, adults 0.117
- O. mossambicus: children 0.239, adults 0.136
- L. calcarifer: children 0.198, adults 0.113
All THQ values <1 for all metals in all species.
Cancer risk (CR) for As (Table 5):
- N. japonicus: children 1.73×10⁻⁶, adults 9.90×10⁻⁷ — borderline threshold
- O. mossambicus: children 1.23×10⁻⁶, adults 7.01×10⁻⁷
- L. calcarifer: children 7.93×10⁻⁷, adults 4.53×10⁻⁷
Cancer risk for Cr (total Cr, not speciated to Cr-VI):
- N. japonicus children: 1.02×10⁻⁶
- O. mossambicus children: 1.91×10⁻⁶
- Authors explicitly note that Cr values reflect total chromium without differentiation of Cr(III) vs Cr(VI); the Cr(VI) fraction is unknown.
Lead EDI (µg/kg/day, muscle, adults): 33.3–37.8 µg/kg/day — elevated compared to similar studies.
Exposure parameters: IR 150 g/day adults, 75 g/day children; BW 70 kg adults, 20 kg children; EFr 365 days/yr; ED 70 yr.
Methods (brief)
ICP-MS (Perkin Elmer NexION 1000) at Vellore Institute of Technology, India; helium KED mode; RF 1600 W. Acid digestion: 25 mg dried tissue in 8 mL 65% HNO₃ + 1 mL 30% H₂O₂ at 220°C for 8 h. Calibration curves for As, Cd, Cr, Pb, Sr, V: 0.01–100 µg/L; for Hg: 0.005–50 µg/L; all R² >0.999. RSD <5% (triplicate measurement). LOD 0.001–0.010 µg/kg; LOQ 0.005–0.030 µg/kg.
Speciation note: Hg is reported as total mercury (tHg), not as methylmercury (MeHg). As is reported as total arsenic (tAs). Cr is reported as total chromium; no Cr-VI speciation performed.
Basis: dry weight throughout (samples dehydrated in hot-air oven at 40–50°C to constant weight before digestion).
Sample size: n=18 total (6 per species), which the authors identify as a primary limitation.
Implications
Certification: This paper documents Pb-dominant contamination in industrially-impacted Indian coastal fish at concentrations (15–18 µg/kg dry weight muscle) that are environmentally elevated but below typical EU/Codex limits when converted to wet weight (roughly 3–4 µg/kg wet weight). The total Hg values (0.020–0.066 µg/kg dry weight) are very low; no MeHg speciation was performed.
Courses: Useful case study for industrial-zone seafood contamination in South Asia; illustrates tissue-specific bioaccumulation patterns (liver as primary Pb/Cd accumulation site vs muscle as the consumed tissue).
App: Supports tagging commercially-sourced Indian freshwater and coastal fish (tilapia, barramundi) as moderate Pb sources in industrialized coastal regions. Note the tHg values are extremely low in this dataset; app users in India should not expect this dataset to be representative of MeHg risk from coastal fish generally.